Valve component with improved wear resistance

ABSTRACT

A valve component for a faucet includes a substrate, a first layer of material provided above the substrate in an amount sufficient to improve abrasion resistance of the substrate, and a second layer of material provided above the first layer of material. The second layer of material includes amorphous diamond having sp 3  bonding of at least about 40%, a hardness of at least about 45 GPa, and an elastic modulus of at least about 400 GPa.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/201,395 filed Aug. 10, 2005, which is a Continuation of U.S. patentapplication Ser. No. 10/741,848 filed Dec. 18, 2003 (now U.S. Pat. No.6,935,618), which is a Continuation of U.S. patent application Ser. No.10/322,871 (now U.S. Pat. No. 6,904,935), filed Dec. 18, 2002. Theentire disclosures for each of the following applications areincorporated herein by reference in their entirety: U.S. patentapplication Ser. No. 11/201,395; U.S. patent application Ser. No.10/741,848; and U.S. patent application Ser. No. 10/322,871.

BACKGROUND

This invention relates generally to multi-layer surface coatings for usewith articles of manufacture and products requiring low friction, lowwear, and protective exterior surfaces. More particularly, the inventionis related to articles having mutually sliding components, such as valvecomponents for water mixing valves, having surface protective layerscomprising a strengthening layer and an outer amorphous diamond coating.

In certain applications, such as for example, valve plates for fluidcontrol valves, there is a need for mutually sliding surfaces to be wearresistant, abrasion resistant, scratch resistant, and to have a lowcoefficient of friction. The elements of one type of control valve formixing of hot and cold water streams typically comprise a stationarydisk and a moveable sliding disk, although the plate elements may be ofany shape or geometry having a sealing surface, including e.g. flat,spherical, and cylindrical surfaces. The term “disk” herein thereforerefers to valve plates of any shape and geometry having mating surfaceswhich engage and slide against each other to form a fluid-tight seal.The stationary disk typically has a hot water inlet, a cold water inlet,and a mixed water discharge outlet, while the moveable disk containssimilar features and a mixing chamber. It is to be understood that themixing chamber need not be in the disk but could part of an adjacentstructure. The moveable disk overlaps the stationary disk and may beslid and/or rotated on the stationary disk so that mixed water at adesired temperature and flowrate is obtained in the mixing chamber byregulating the flowrate and proportions of hot water and cold wateradmitted from the hot water inlet and the cold water inlet anddischarged through the mixed water discharge outlet. The disks matingsealing surfaces should be fabricated with sufficient precision to allowthe two sealing surfaces to mate together and form a fluid tight seal(i.e. they must be co-conformal and smooth enough to prevent fluid frompassing between the sealing surfaces). The degree of flatness (for aflat plate shape), or co-conformity (for non-flat_surfaces) andsmoothness required depend somewhat on the valve construction and fluidsinvolved, and are generally well known in the industry. Other types ofdisk valves, while still using mating sealing surfaces in slidingcontact with each other, may control only one fluid stream or mayprovide mixing by means of a different structure or port configuration.The stationary disk may for example be an integral part of the valvebody.

Previous experience with this type of control valve has demonstratedthere is a problem of wear of the mating surfaces of the disks due tothe fact that the stationary and moveable disks are in contact and slideagainst each other (see for example U.S. Pat. Nos. 4,935,313 and4,966,789). In order to minimize the wear problem, these valve disks areusually made of a sintered ceramic such as alumina (aluminum oxide).While alumina disks have good wear resistance, they have undesirablefrictional characteristics in that operating force increases, and theytend to become “sticky” after the lubricant grease originally applied tothe disks wears and washes away. The scratch and abrasion resistance ofalumina plates to large and small particles (respectively) in the waterstream is good; however, they are still susceptible to damage fromcontaminated water streams containing abrasive particles such as sand;and improvement in this regard would be beneficial. Additionally, theporous nature of the sintered ceramic disks makes them prone to “lockup”during long periods of non-use, due to minerals dissolved in the watersupply that precipitate and crystallize between coincident pores in themating surfaces. One objective of the present invention is to providedisks having reduced wear, improved scratch and abrasion resistance andreduced frictional characteristics. Another objective is to providenon-porous or reduced-porosity valve disks to reduce the number oflocations where precipitated crystals may form between the matingsurfaces.

It would be advantageous to use a material for the disks, such as metal,which is less expensive, easier to grind and polish and which is notporous. However, the wear resistance and frictional behavior of baremetallic disks is generally not acceptable for sliding sealapplications. A further objective of the present invention is to providedisks made of metal a base material and having improved wear, scratch,and abrasion resistance and improved frictional characteristics ascompared to uncoated ceramic disks.

It is disclosed in the prior art (e.g. U.S. Pat. Nos. 4,707,384 and4,734,339, which are incorporated herein by reference) thatpolycrystalline diamond coatings deposited by chemical vapor deposition(CVD) at substrate temperatures around 800-1000 C can be used incombination with adhesion layers of various materials in order toprovide scratch and wear resistant components. Polycrystalline diamondfilms, however, are known to have rough surfaces due to the crystalfacets of the individual diamond grains, as is apparent in thephotographs of FIGS. 2 and 3 in the '384 patent. It is known in the artto polish such surfaces in order to minimize the coefficient of frictionin sliding applications, or even to deposit the polycrystalline diamondon a smooth substrate and then remove the film from the substrate anduse the smooth side of the film (which was previously against thesubstrate) rather than the original surface as the bearing surface. Thepresent invention overcomes prior art problems by providing a number ofadvantageous features, including without limitation providing a smoothand very hard surface for sliding applications, while avoiding difficultand expensive post-processing of a polycrystalline diamond surfacelayer. The methodology also advantageously employs substrate materials(such as, suitable metals, glasses, and composite and organic materials)that cannot be processed at the elevated temperatures necessary for CVDdeposition of polycrystalline diamond.

It is also disclosed in the prior art (e.g. U.S. Pat. No. 6,165,616,which is incorporated herein by reference) that engineered interfacelayers may be employed to relieve thermally-induced stress in apolycrystalline diamond layer. These thermally induced stresses ariseduring cooling of the substrate after coating deposition at relativelyhigh temperatures, and are due to the difference in thermal expansioncoefficient between the substrate and the diamond coating. Rathercomplicated engineering calculations are specified in '616 topredetermine the desired interface layer composition and thickness. Theinterface layer thickness' disclosed in '616 to minimize thethermally-induced stress in the diamond layer are of the order 20 to 25microns according to FIGS. 1 through 3. Such thick interface layers areexpensive to deposit, due to the time necessary to deposit them and thehigh cost of the equipment required. The present invention alsoadvantageously includes, without limitation, minimizing the coating costbut still achieving desired results by employing much thinner interfacelayers than those taught by '616, and to avoid creating thethermally-induced stresses which necessitate such complicatedengineering calculations by depositing a hard surface layer at arelatively low temperature compared to the prior art, such as the '616patent.

It is further disclosed in the prior art (e.g. U.S. Pat. Nos. 4,935,313and 4,966,789, which are incorporated herein by reference) that cubiccrystallographic lattice carbon (polycrystalline diamond) and other hardmaterials may be used as surface coatings on valve disks, and that pairsof mutually sliding valves discs which differ from each other in eithersurface composition or surface finish are preferable to those which arethe same in these characteristics, with respect to minimizing frictionbetween the plates. The present invention provides mating valve disksurfaces having a lower friction coefficient than the disclosedmaterials in water-lubricated or fluid wetted surface applications suchas water valves, and to allow identical processing of both matingsurfaces in order to avoid the need to purchase and operate differenttypes of processing equipment. The present invention further provides,without limitation, mating valve disk surfaces having a lower frictioncoefficient than the disclosed materials in water-lubricated or fluidwetted surface applications such as water valves. Furthermore, bothmated sliding surfaces of the disks can be hard and have an abrasionresistance to contaminated water streams and to allow identicalprocessing of both mating surfaces in order to avoid the need topurchase and operate different types of processing equipment.

SUMMARY

An exemplary embodiment relates to a valve component for a faucet thatincludes a substrate, a first layer of material provided above thesubstrate in an amount sufficient to improve abrasion resistance of thesubstrate, and a second layer of material provided above the first layerof material. The second layer of material includes amorphous diamondhaving sp bonding of at least about 40%, a hardness of at least about 45GPa, and an elastic modulus of at least about 400 GPa.

Another exemplary embodiment relates to a faucet that includes a firstvalve plate comprising a base material, a strengthening layer providedabove the base material, and an amorphous diamond material providedabove the strengthening layer. The amorphous diamond material has acoefficient of friction that is lower than that of diamond-like carbonand has a hardness that is greater than that of diamond-like carbon.

Another exemplary embodiment relates to a faucet valve plate thatincludes a substrate, a layer of material comprising at least onematerial selected from the group consisting of chromium nitride anddiamond-like carbon provided above the substrate, and an amorphousdiamond layer provided above the layer of material, the amorphousdiamond layer having a hardness that is greater than that ofdiamond-like carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one form of valve incorporating a multi-layer structure withan amorphous diamond layer overlying a substrate;

FIG. 2 is a detail of one form of multi-layer structure of theinvention;

FIG. 3 illustrates yet another multi-layer structure with an addedadditional adhesion-promoting layer;

FIG. 4 is a further form of multi-layer structure of FIG. 2 wherein astrengthening layer includes two layers of different materials; and

FIG. 5 is a photomicrograph of the surface appearance of an exterioramorphous diamond layer over an underlying substrate or layer.

DETAILED DESCRIPTION

Embodiments of the invention are illustrated generally in the figures,where FIG. 1 shows one form of the valve 10 with handle 12 incorporatingthe invention. In particular, FIGS. 2-4 illustrate a portion of a valve10 having a substrate 18 for a sliding component 20 and/or a fixedcomponent 22 of the valve 10 which can comprise a base material whereinthe base material can be the same or different in the sliding component20 and the fixed component 22. In other embodiments, one of thecomponents 20, 22 can be fixed. Preferably the base material is asintered ceramic or a metal. Base materials can also comprise glasses orglassy materials, cermets, polymeric materials, composite materials,intermetallic compounds such as iron aluminide, and other materialsmechanically suitable for the application. The metals can include, forexample, any conventional metal, including without limitation, stainlesssteel, brass, zirconium, titanium, aluminum, and alloys of the latterthree materials. Stainless steel, titanium, and zirconium, and aluminumare the most preferred metals, with the term stainless steel referringto any type such as 304, 316, etc., and customized variations thereofand with the terms titanium, zirconium, and aluminum understood toinclude alloys comprised mostly of those metals. Sintered (powdered)stainless steel is a preferred substrate material because it can beeconomically molded into complex shapes suitable for disks and can beeconomically ground and polished to achieve a mating smooth sealingsurface. In the case of sintered stainless steel, “fully dense”substrates and metal injection molded substrates are preferred. Titaniumand zirconium are preferred base materials because they can be easilyoxidized or anodized to form a hard surface layer. Ceramics can be anyconventional ceramic material, including without limitation, forexample, sintered alumina (aluminum oxide) and silicon carbide, withalumina being a preferred material. Composite materials can include, forexample, any conventional cermets, fiber reinforced epoxies andpolyamides, and carbon-carbon composites. Glass and glassy materials caninclude for example borosilicate glass such as Pyrex™, and materialssuch as toughened laminated glass and glass-ceramics. Glass, glassymaterials and cermets are preferred substrates because they can beeconomically molded into complex shapes suitable for disks and can beeconomically ground and polished to a flat and smooth surface. Ironaluminide is understood to be a material consisting mainly of that ironand aluminum but may also contain small amounts of such other elementsas molybdenum, zirconium, and boron.

As shown in FIG. 2, a strengthening layer 23 can also be placed directlyon the substrate surface 18. This layer 23 can comprise a materialhaving higher hardness than the substrate 18. Suitable materials for thestrengthening layer 23 can include compounds of Cr, Ti, W, Zr, and anyother metals conventionally known for use in hard coatings. Thecompounds include without limitation are nitrides, carbides, oxides,carbo-nitrides, and other mixed-phase materials incorporating nitrogen,oxygen, and carbon. One highly preferred material for the strengtheninglayer 23 is chromium nitride. Chromium nitride in the presentapplication most preferably refers to a single or mixed phase compoundof chromium and nitrogen having nitrogen content in the range of about10 to about 50 atomic percent. The term chromium nitride also refers toa material containing such doping or alloying elements as yttrium,scandium, and lanthanum in addition to chromium and nitrogen.

Another material suitable for the strengthening layer 23 is conventionalDLC (Diamond-Like Carbon), which is a form of non-crystalline carbonwell known in the art and distinct from amorphous diamond. DLC coatingsare described for example in U.S. Pat. No. 6,165,616 (in which they arecalled (a-C) coatings). DLC can be deposited by sputtering or byconventional CVD. DLC is an amorphous material with mostly sp2 carbonbonding and little of the tetrahedral sp3 bonding that characterizesamorphous diamond. The hardness of DLC is substantially lower than thatof amorphous diamond and is more similar to the hardness of conventionalhard coating materials such as titanium nitride and chromium nitride.The internal stresses in DLC coatings are also lower than those inamorphous diamond coatings, allowing DLC to be deposited in thickerlayers than amorphous diamond without loss of adhesion. The term DLC asused herein includes hydrogenated forms of the material.

The strengthening layer 23 functions primarily to improve scratch andabrasion resistance of the multilayer coating. The hardness of thestrengthening layer 23 should be at least greater than that of thesubstrate 18 in order to perform its intended function of improving thescratch resistance of the coated disk. The thickness of thestrengthening layer 23 is at least a thickness sufficient to improve thescratch resistance of the substrate 18. For materials typically used ashard coatings, such as those disclosed above, this thickness isgenerally from around 500 nm to around 10 microns, and preferably fromabout 2000 nm to around 5000 nm. In testing of faucet water valves ithas been found that a chromium nitride strengthening layer having athickness of about 5 microns provides adequate scratch and abrasionresistance (in conjunction with a thin amorphous diamond top layer) fortypes and sizes of contaminants considered to be typical in municipaland well water sources.

In some embodiments of the present invention as shown in FIG. 3 and forcomponent 22 of FIG. 4, a thin adhesion-promoting layer 21 can bedeposited on the substrate 18 and then the strengthening layer 23 on thelayer 21. This layer 21 functions to improve the adhesion of theoverlying strengthening layer 23 to the substrate 18. Suitable materialsfor the adhesion-promoting layer 21 include preferably chromium and alsocan include titanium, tungsten, other refractory metals, silicon, andother materials known in the art to be suitable as adhesion-promotinglayers. The layer 21 can conveniently be made using the same elementalmaterial chosen for the strengthening layer 23. The layer 21 has athickness that is at least adequate to promote or improve the adhesionof layer 23 to the substrate 18. This thickness is generally from about5 nm to about 200 nm, and most preferably from about 30 nm to about 60nm. The adhesion-promoting layer 21 can be deposited by conventionalvapor deposition techniques, including preferably physical vapordeposition (PVD) and also can be done by chemical vapor deposition(CVD).

PVD processes are well known and conventional and include cathodic arcevaporation (CAE), sputtering, and other conventional depositionprocesses. CVD processes can include low pressure chemical vapordeposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD),and thermal decomposition methods. PVD and CVD techniques and equipmentare disclosed, inter alia, in J. Vossen and W. Kern “Thin Film ProcessesII”, Academic Press, 1991; R. Boxman et al, “Handbook of Vacuum ArcScience and Technology”, Noyes, 1995; and U.S. Pat. Nos. 4,162,954 and4,591,418, with the patents incorporated herein by reference.

In the case of sintered ceramic materials, although the individualgranules forming the sintered material may have high hardness, thescratch resistance of the overall sintered structure as measured byscratch testing is much lower than that of the material forming thegranules (e.g. alumina). This is due to the fact that the materialstypically used to sinter or bond the alumina granules together,typically silicates, are not as hard as the granules themselves. Thehardness of the strengthening layer 23 can be similar to or even lessthan the hardness of the individual granules comprising the ceramicdisk, and still being harder than the overall sintered ceramicstructure. It has been found by experiment, for example, that the depthof the scratch caused by a stylus (radius=100 microns) sliding under aload of 30 Newtons is approximately 4-6 microns on an uncoated sinteredalumina substrate, while the scratch depth on an identical substratecoated with a 3 micron thick chromium nitride strengthening layer isonly 2-3 microns.

The strengthening layer 23 can be formed by conventional vapordeposition techniques including, but not limited to sputtering, cathodicarc evaporation (CAE), and CVD. The most preferred methods aresputtering, CAE, or other means which may be carried out at a relativelylow temperature, thereby minimizing thermally-induced stresses in thecoating stack upon cooling. If the strengthening layer 23 is depositedby CAE, it is also desirable to use macroparaticle filtering in order tocontrol and to preserve the smoothness of the surface of the substrate18. The strengthening layer 23 can also be formed by other well-knownmethods for forming hard coatings such as spray pyrolysis, sol-geltechniques, liquid-dipping with subsequent thermal treatment,nano-fabrication methods, atomic-layer deposition methods, andmolecular-layer deposition methods.

The strengthening layer 23 can alternatively be formed by a process thatproduces a hardened surface layer on the substrate base material. Suchprocesses include, for example, thermal oxidation, plasma nitriding, ionimplantation, chemical and electrochemical surface treatments such aschemical conversion coatings, anodizing including hard anodizing andconventional post-treatments, micro-arc oxidation and case hardening.The strengthening layer 23 can also include multiple layers 24 and 25 asshown in FIG. 4, in which the layers 24 and 25 together form thestrengthening layer 23. For example, the layer 24 can be an oxidethermally grown on the substrate base material while the layer 25 is adeposited material such as CrN. The strengthening layer 23 can alsoinclude more than two layers, and can preferably comprise for example asuperlattice type of coating with a large number of very thinalternating layers. Such a multilayer or superlattice form of thestrengthening layer 23 can also include one or multiple layers ofamorphous diamond.

In the multi-layer structure of FIGS. 1-4 the amorphous diamond layer 30is deposited over the strengthening layer 23 to form an exterior surfacelayer. The purpose of the amorphous diamond layer 30 is to provide avery hard wear abrasion resistant and lubricous top surface on thesliding components. Amorphous diamond is a form of non-crystallinecarbon that is well known in the art, and is also sometimes referred toas tetrahedrally-bonded amorphous carbon (taC). It can be characterizedas having at least 40 percent sp3 carbon bonding, a hardness of at least45 gigaPascals and an elastic modulus of at least 400 gigaPascals.Amorphous diamond materials are described in U.S. Pat. Nos. 5,799,549and 5,992,268, both of which are incorporated herein by reference. Theamorphous diamond material layer 30 can be applied processes including,for example, conventional filtered cathodic arc evaporation and laserablation. The term amorphous diamond as used herein includes all formsof taC type carbon and may also contain doping or alloying elements suchas nitrogen and metals, and also includes nano-structured materialscontaining amorphous diamond. Nano-structured materials mean hereinmaterials having structural features on the scale of nanometers or tensof nanometers, including but not limited to superlattices.

The thickness of the amorphous diamond layer 30 is at least a valueeffective to provide improved wear and abrasion resistance of thesliding component. This thickness is generally at least about 100 nm,preferably at least about 200 nm and more preferably at least about 300nm. The upper thickness range of the layer 30 is determined by materialcharacteristics, economic considerations and the need to minimizethickness-dependent intrinsic stresses in the layer 30 as discussedbelow. Also amorphous diamond layer 30 advantageously exhibits anextremely smooth surface topology as can be seen by reference to thephoto of FIG. 5, principally because there are no individual diamondgrains in an amorphous coating. In addition, the surface topography ofthe thin amorphous diamond layer 30 essentially replicates that of thesubsurface upon which it is deposited, and therefore the amorphousdiamond layer 30 has substantially the same average surface roughness asthat of the subsurface. Graphitic inclusions, visible as light spots inFIG. 5, do not contribute to the surface roughness, as the term is usedherein, because they are very soft and are reduced to a lubricativepowder when the sliding surfaces are brought into contact. Amorphousdiamond has the further advantage that it can be deposited at much lowertemperatures (generally below approximately 250 C) than polycrystallinediamond, thus eliminating the need for the thick, engineered interfacelayers disclosed in the prior art (see, e.g. U.S. Pat. No. 6,165,616)for relieving the thermally-induced stress in the diamond layer. Thesethermally induced stresses arise during cooling after deposition at thehigh temperatures characteristic of CVD, and are due to the differencein thermal expansion coefficient between the substrate and the diamondcoating. We have found that the type of calculations disclosed in the'616 patent for determining the thickness of its thermally-inducedstress relieving interface layer are not necessary for amorphous diamondfilms due to the low deposition temperature.

One characteristic of amorphous diamond is that it develops highintrinsic (non-thermally-induced) internal stresses, which increase asthe coating thickness increases and which are predominately related toatomic bonding distortions and not to thermal expansion/contraction.While this intrinsic stress is believed to contribute to the highhardness of the material, it also limits the coating thickness sincestress-induced forces tend to cause delamination of the coating from thesubstrate 18 (or the strengthening layer 23) above a certain thickness.Although amorphous diamond can be deposited directly on a metal, glassor iron aluminide disk (optionally with an adhesion layer), it isdifficult to deposit a thick enough layer to provide adequate scratchresistance for water valve applications. Scratch resistance is importantbecause water supplies sometimes contain abrasive contaminants due topipeline breaks, construction, etc. The additional strengthening layer23 of the present invention provides better support of the amorphousdiamond layer 30 than does the softer substrate material, advantageouslyallowing a thinner layer of amorphous diamond to be used, while stillobtaining improved scratch and abrasion resistance. The strengtheninglayer 23 can also be chosen to be a material that has a greaterdeposition rate and/or is less expensive to deposit than the amorphousdiamond layer 30, in order to minimize overall coating cost whilemaintaining performance. In the most preferred embodiment, an upperthickness limit for the amorphous diamond layer 30 of around 1-2 micronscan be used to avoid stress-induced delamination, while an upperthickness of around 800 nm, and more preferably around 300-500 nm, canbe desirable for economic reasons while still achieving the desiredperformances characteristics.

Amorphous diamond is well suited to wet sliding applications in watervalve applications. In particular it has been shown to have a very lowcoefficient of friction and also extremely low abrasion wear inwater-lubricated sliding tests in which both sliding surfaces are coatedwith amorphous diamond. In contrast, DLC coatings are known to havehigher friction coefficients higher wear rates, and to deteriorate infrictional performance with increasing humidity. A further advantage ofamorphous diamond is that the relatively low deposition temperatureallows a wider choice of substrate materials and minimizes or eliminatespermanent thermally induced distortion of the substrate.

Regarding the low coefficient of friction reported for amorphous diamondcoatings in water-lubricated sliding tests, it is thought that this maybe due at least in part to graphitic inclusions (commonly calledmacroparticles) that are incorporated in amorphous diamond coatings madeby some methods. Such graphitic inclusions can be numerous in carboncoatings deposited by cathodic arc evaporation, depending on the choicetarget materials and use of macroparticle filtering means as discussedbelow. These graphitic inclusions do not degrade the performance of theamorphous diamond coating due their softness and the small fraction ofthe total surface area they occupy. Rather, it is thought that they mayimprove performance by increasing lubricant retention between thesliding plates.

It is disclosed in U.S. Pat. No. 5,401,543 (incorporated herein byreference) that amorphous diamond coatings which are essentially free ofmacroparticles can be deposited by cathodic arc evaporation from avitreous carbon or pyrolytic graphite cathode. The maximum density ofmacroparticles (graphitic inclusions) in such coatings, as calculatedfrom the areal dimensions of the photographic figures and themacroparticle counts disclosed, is around 200 macroparticles per squaremillimeter. Such macroparticle-free amorphous diamond coatings can beused as layer 30 in the present invention, but are less-preferred thanthose deposited from an ordinary graphite cathode and containingsubstantial numbers of graphitic inclusions, such as, for example, atleast about 500 per square millimeter. They are also less preferredbecause the required vitreous carbon or pyrolytic graphite cathodes arequite expensive compared to ordinary graphite.

The number of graphitic inclusions 40 incorporated into coatings (seeFIG. 4 showing them schematically) deposited by filtered arc evaporationfrom an ordinary graphite cathode can be controlled according to thepresent invention by choosing the filter design and operating parametersso as to allow the desired number of macroparticles to be transmittedthrough the source. The factors influencing the transmission ofmacroparticles through a filter are discussed e.g. in U.S. Pat. No.5,840,163, incorporated herein by reference. Filter designs andoperating parameters are conventionally chosen to minimize the number ofmacroparticles transmitted through the source, however this choice alsogenerally reduces the (desired) output of carbon ions and hence reducesthe deposition rate. Contrary to this usual practice, we find that it ispreferable for purposes of minimizing coating cost to choose the filterdesign and operating parameters so as to maximize the carbon ion outputof the source (i.e. the deposition rate) without exceeding the maximumtolerable number of graphitic inclusions incorporated into the coating.The maximum tolerable number of inclusions is that number above whichthe performance of the coated parts deteriorates unacceptably due to theincreasing fraction of the surface area occupied by the inclusions.Critical performance factors can include non-leakage of the workingfluid, sliding friction coefficient, scratch and abrasion resistance,and wear life. We have found that graphitic inclusion surface densitiessubstantially higher than 500/mm² are tolerable, and may be beneficialas described above.

The adhesion of the amorphous diamond layer 30 to a nitride form of thestrengthening layer 23 can in some cases be improved by the introductionof a carbon-containing gas, such as methane, during a short period atthe end of the deposition of the strengthening layer 23. This results ina thin transition zone of carbo-nitride and/or carbide material betweenthe strengthening layer 23 and the amorphous diamond layer 30. In othercases the adhesion can be improved by turning off all reactive gassesduring a short period at the end of the deposition of the strengtheninglayer 23. This results in a thin metal layer between the strengtheninglayer 23 and the amorphous diamond layer 30. It has also been noted thatthe introduction of methane during the filtered-arc deposition of theamorphous diamond layer 30 increases the coating deposition rate, andcan also improve the coating hardness and scratch resistance. In stillother cases, for example the case in which the amorphous diamond layer30 is to be deposited on a thermally oxidized metal surface, it can bedesirable to deposit the separate adhesion-promoting layer 21 betweenthe strengthening layer 23 and the amorphous diamond layer 30. Suitablematerials for the adhesion layer 21 can include for example refractorycarbide-forming metals, such as, Ti and W, and various transition metalssuch as Cr, and can also include carbides of those metals.

In order that the invention may be more readily understood the followingexamples are provided. The examples are illustrative and do not limitthe invention to the particular features described.

EXAMPLE 1

Clean stainless steel valve disks are placed in a vacuum depositionchamber incorporating an arc evaporation cathode and a sputteringcathode. The arc source is fitted with filtering means to reducemacroparticle incorporation in the coating, as described for example inU.S. Pat. Nos. 5,480,527 and 5,840,163, incorporated herein byreference. Sources of argon and nitrogen are connected to the chamberthrough a manifold with adjustable valves for controlling the flowrateof each gas into the chamber. The sputtering cathode is connected to thenegative output of a DC power supply. The positive side of the powersupply is connected to the chamber wall. The cathode material ischromium. The valve disks are disposed in front of the cathode, and maybe rotated or otherwise moved during deposition to ensure uniformcoating thickness. The disks are electrically isolated from the chamberand are connected through their mounting rack to the negative output ofa power supply so that a bias voltage may be applied to the substratesduring coating.

Prior to deposition the vacuum chamber is evacuated to a pressure of2×10e-5 Torr or less. Argon gas is then introduced at a rate sufficientto maintain a pressure of about 25 milliTorr. The valve disks are thensubjected to a glow discharge plasma cleaning in which a negative biasvoltage of about 500 volts is applied to the rack and valve disks. Theduration of the cleaning is approximately 5 minutes.

A layer of chromium having a thickness of about 20 nm is then depositedon the valve disks by sputtering. After the chromium adhesion layer isdeposited, a strengthening layer of chromium nitride having a thicknessof about 3 microns is deposited by reactive sputtering.

After the chromium nitride layer is deposited, the valve disks aredisposed facing the arc source, and a top amorphous diamond layer havinga thickness of about 300 nm is deposited by striking an arc on thecarbon electrode and exposing the substrates to the carbon plasmaexiting the source outlet. A negative DC bias of about 500 volts isinitially applied to the substrates to provide high-energy ionbombardment for surface cleaning and bonding improvement. After about 5minutes at high bias voltage, the bias voltage is reduced to about 50volts for the remainder of the deposition process. An argon pressure ofabout 0.5 milliTorr is maintained in the chamber during deposition.Pulsed or AC bias voltages may alternatively be employed, and a higheror lower argon may also be maintained in order to stabilize the arcsource operation and optimize coating properties.

It has been found by experiment that valve disks made of stainless steeland coated according to the above example were able to withstand morethan 15,000 test cycles in circulating water carrying 20 micron silicasand, while standard uncoated alumina valve disks failed under the sameconditions in less than 2500 cycles.

EXAMPLE 2

Clean zirconium valve disks are placed into an air oven, heated to atemperature of 560 C, held at this temperature for about 6 hours, andcooled. A strengthening layer of zirconium oxide is thereby formed onthe substrate surface, having a thickness of 5-10 microns. The disks arethen placed in a vacuum deposition chamber incorporating a filtered arcevaporation cathode and a sputtering cathode. An adhesion layer ofchromium having a thickness of about 20 nm is deposited on the valvedisks by sputtering as described in example 1. After the chromiumadhesion layer is deposited, an amorphous diamond layer is deposited asdescribed in Example 1.

Valve disks made of zirconium and treated as described to form amultilayer structure on their surfaces were tested for scratchresistance, using a scratch tester with variable loading. The scratchdepths generated on the treated Zr disks by a stylus tip having 100micron radius under a load of 3 Newtons were around 4.7 microns deep,while those on untreated Zr disks were about 9.5 microns or more thantwice as deep. Scratch test performance is believed to be a relevantpredictor of scratch and abrasion resistance in field applications.

EXAMPLE 3

Clean molded-glass valve disks are placed in a vacuum deposition chamberincorporating a laser ablation source, a PECVD source, and a sputteringcathode. The valve disks are subjected to a RF (radio-frequency)discharge plasma cleaning by known means. An adhesion layer of titaniumhaving a thickness of about 20 nm is then deposited on the valve disksby sputtering. A strengthening layer of DLC having thickness of about 3microns is then deposited on top of the adhesion layer by PECVD usingknown deposition parameters. An amorphous diamond layer having thicknessof about 300 nm is then deposited on top of the DLC layer by laserablation using typical deposition parameters.

EXAMPLE 4

Clean stainless steel valve disks are placed in a vacuum chambercontaining a filtered arc evaporation source and a sputtering cathode.The chamber is evacuated, nitrogen gas is introduced, a plasma dischargeis established between the disks and the chamber walls, and the disksurface is plasma-nitrided according to known parameters. Nitrogendiffuses into the stainless substrates to form a surface layer harderthan the bulk substrate, and the process is continued for a period oftime sufficient for the layer depth to reach about 2 microns. Asuperlattice consisting of multiple alternating layers of carbon nitrideand zirconium nitride is then deposited on the nitrided stainless steelsurface by filtered arc evaporation and sputtering respectively. Thealternating individual layers are about 10 nm thick, and about 100layers of each material is deposited for a total superlattice thicknessof about 2 microns. The ratio of nitrogen to carbon in the carbonnitride layers is preferably around 1.3, since carbon nitride+zirconiumnitride superlattices having this N:C ratio have been shown to haveprimarily sp3-bonded carbon and hardness in the range of 50 gigaPascals.Carbon nitride as used herein refers to a material having a N:C ratiobetween about 0.1 and 1.5.

The large number of thin layers may conveniently be deposited bymounting the substrate on a rotating cylinder such that the substratespass first in front of one deposition source and then the other, suchthat one pair of layers is deposited during each revolution of thecylinder. The total strengthening layer thickness is about 4 micronsincluding the plasma-nitrided stainless steel layer. An amorphousdiamond layer having thickness of about 200 nm is then deposited on topof the superlattice layer by filtered arc evaporation as described inExample 1.

The construction and arrangement of the elements shown in the preferredand other exemplary embodiments is illustrative only. Although only afew embodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, use of materials, etc.) without materiallydeparting from the novel teachings and advantages of the subject matterrecited herein. The order or sequence of any process or method steps maybe varied or re-sequenced according to alternative embodiments. Othersubstitutions, modifications, changes and omissions may be made in thedesign, operating conditions and arrangement of the preferred and otherexemplary embodiments without departing from the scope of the presentinvention.

1. A valve component for a faucet comprising: a substrate; a first layerof material provided above the substrate in an amount sufficient toimprove abrasion resistance of the substrate; and a second layer ofmaterial provided above the first layer of material, the second layer ofmaterial comprising amorphous diamond having sp³ bonding of at leastabout 40%, a hardness of at least about 45 GPa, and an elastic modulusof at least about 400 GPa.
 2. The valve component of claim 1, whereinthe second layer of material has a coefficient of friction that is lowerthan that of diamond-like carbon.
 3. The valve component of claim 1,wherein the second layer of material has a hardness that is higher thanthat of diamond-like carbon.
 4. The valve component of claim 1, whereinthe second layer of material consists essentially of carbon.
 5. Thevalve component of claim 1, wherein the first layer of materialcomprises diamond-like carbon, the diamond-like carbon having a hardnessless than that of amorphous diamond.
 6. The valve component of claim 1,wherein the first layer of material comprises chromium nitride.
 7. Thevalve component of claim 1, wherein the first layer of materialcomprises a compound of at least one of chromium, titanium, tungsten,and zirconium, the compound comprising one of a nitride, a carbide, anoxide, and a carbo-nitride.
 8. The valve component of claim 1, whereinthe first layer of material comprises a plurality of superlatticelayers.
 9. The valve component of claim 1, wherein the first layer ofmaterial has a hardness that is greater than that of the substrate. 10.The valve component of claim 1, wherein the substrate comprises a metalselected from the group consisting of stainless steel, aluminum, brass,titanium and zirconium.
 11. The valve component of claim 1, wherein thesubstrate comprises a material selected from the group consisting of aglass, a cermet, a glass containing material, a polymeric material and acomposite material.
 12. The valve component of claim 1, wherein thesecond layer of material comprises a plurality of layers of differentphases of diamond, wherein at least one of the plurality of layerscomprises amorphous diamond.
 13. The valve component of claim 1, whereinthe second layer of material has a thickness less than about 10 microns.14. The valve component of claim 13, wherein the first layer of materialhas a thickness of between approximately 500 nanometers and 6 microns.15. The valve component of claim 1, wherein the first layer of materialincludes a dopant of at least one of nitrogen and a metal.
 16. The valvecomponent of claim 1, further comprising an adhesion-promoting layerprovided between the first and second layers of material.
 17. The valvecomponent of claim 16, wherein the adhesion-promoting layer comprises atleast one material selected from the group consisting of chromium,titanium, tungsten, and silicon.
 18. A valve component for a faucetcomprising: a substrate; a first layer of material provided above thesubstrate in an amount sufficient to improve abrasion resistance of thesubstrate, the first layer of material having a hardness greater thanthat of the substrate; and a second layer of material provided above thefirst layer of material, the second layer of material comprisingamorphous diamond having sp³ bonding of at least about 40%, a hardnessof at least about 45 GPa, and an elastic modulus of at least about 400GPa; wherein the second layer of material has a coefficient of frictionthat is lower than that of diamond-like carbon and a hardness that ishigher than that of diamond-like carbon.
 19. The valve component ofclaim 18, wherein the second layer of material consists essentially ofcarbon.
 20. The valve component of claim 18, wherein the first layer ofmaterial comprises at least one material selected from the groupconsisting of diamond-like carbon and chromium nitride.
 21. The valvecomponent of claim 18, wherein the first layer of material comprises acompound of at least one of chromium, titanium, tungsten, and zirconium,the compound comprising one of a nitride, a carbide, an oxide, and acarbo-nitride.
 22. The valve component of claim 18, wherein the firstlayer of material comprises a plurality of superlattice layers.
 23. Thevalve component of claim 18, wherein the substrate comprises a materialselected from the group consisting of stainless steel, aluminum, brass,titanium, zirconium, a glass, a cermet, a glass containing material, apolymeric material, and a composite material.
 24. The valve component ofclaim 18, wherein the second layer of material comprises a plurality oflayers of different phases of diamond, wherein at least one of theplurality of layers comprises amorphous diamond.
 25. The valve componentof claim 18, wherein the second layer of material has a thickness lessthan about 10 microns and the first layer of material has a thickness ofbetween approximately 500 nanometers and 6 microns.
 26. The valvecomponent of claim 18, wherein the first layer of material includes adopant of at least one of nitrogen and a metal.
 27. The valve componentof claim 18, further comprising an adhesion-promoting layer providedbetween the first and second layers of material.
 28. The valve componentof claim 27, wherein the adhesion-promoting layer comprises at least onematerial selected from the group consisting of chromium, titanium,tungsten, and silicon.